Flexible membranes

ABSTRACT

Described is a membrane comprising a microlayer polymeric composite having at least about 10 microlayers. The microlayers are each individually up to about 100 microns thick and alternate between at least one gas barrier material and at least one elastomeric material. The membrane can be formed into a pressurized bladder or cushioning device for many applications, including footwear and hydropneumatic accumulators.

FIELD OF THE INVENTION

The present invention concerns membranes suitable for applications thatrequire both barrier properties and flexibility. The membranes of theinvention are particularly useful in construction of pressurizedbladders, including cushioning devices. The membranes of the inventionare elastic and have very low gas transmissions rates for nitrogen andother gasses that can be used to inflate the bladders and cushioningdevices. The present invention further relates to footwear that includesone or more bladders or cushioning devices of the invention.

BACKGROUND OF THE INVENTION

Thermoplastic and thermoset polymeric materials have been widely used inmembranes for their fluid (gas or liquid) barrier properties. Such fluidbarrier films are used, for example, for plastic wrap materials and forother packaging materials. Another common application for polymericmaterials with good fluid barrier properties is in the construction ofinflatable bladders.

Inflatable bladders have been used in a variety of products such asvehicle tires, balls, accumulators used on heavy machinery, and infootwear, especially shoes, as cushioning devices. It is often desirableto use polymeric materials that are thermoplastic because thermoplasticmaterials may be reclaimed and reformed into new articles, thus reducingwaste during manufacturing operations and promoting recycling after thelife of an article. While thermoplastic barrier films may be flexed to acertain extent due to their thinness, thermoplastic barrier films do notgenerally have sufficient elasticity for many applications. Elasticmaterials, or elastomers, are able to substantially recover theiroriginal shape and size after removal of a deforming force, even whenthe part has undergone significant deformation. Elastomeric propertiesare important in many applications, including inflatable bladders forfootwear and hydraulic accumulators.

Footwear, and in particular shoes, usually include two major components,a shoe upper and a sole. The general purpose of the shoe upper is tosnuggly and comfortably enclose the foot. Ideally, the shoe upper shouldbe made from an attractive, highly durable, comfortable materials orcombination of materials. The sole, constructed from a durable material,is designed to provide traction and to protect the foot during use. Thesole also typically serves the important function of providing enhancedcushioning and shock absorption during athletic activities to protectthe feet, ankles, and legs of the wearer from the considerable forcesgenerated. The force of impact generated during running activities canamount to two or three times the body weight of the wearer, while otherathletic activities such as playing basketball may generate forces ofbetween six and ten times the body weight of the wearer. Many shoes,particularly athletic shoes, now include some type of resilient,shock-absorbent material or components to cushion the foot and bodyduring strenuous athletic activity. These resilient, shock-absorbentmaterials or components are commonly referred to in the shoemanufacturing industry as the midsole. Such resilient, shock-absorbentmaterials or components can also be applied to the insole portion of theshoe, which is generally defined as that portion of the shoe upperdirectly underlying the plantar surface of the foot.

Gas-filled bladders may be used for midsoles or inserts within the solesof shoes. The gas-filled bladders are generally inflated to significantpressures in order to cushion against the forces generated on the footduring strenuous athletic activities. Such bladders typically fall intotwo broad categories, those that are "permanently" inflated, such asdisclosed in Rudy, U.S. Pat. No. 4,183,156 and 4,219,945, and thoseusing a pump and valve system, such as those disclosed in Huang, U.S.Pat. No. 4,722,131.

Athletic shoes of the type disclosed in U.S. Pat. No. 4,183,156 having"permanently" inflated bladders have been sold under the trademark"Air-Sole" and other trademarks by Nike, Inc. of Beaverton, Oreg.Permanently inflated bladders of such shoes are constructed using anelastomeric thermoplastic material that is inflated with a largemolecule gas that has a low solubility coefficient, referred to in theindustry as a "super gas." Gases such as SF6, CF₄, C₂ F₆, C₃ F₈, and soon have been used in this way as super gases. Super gases are costly,however, and so it is desirable to provide permanent inflation with lessexpensive gasses like air or nitrogen. By way of example, U.S. Pat. No.4,340,626 entitled "Diffusion Pumping Apparatus Self-Inflating Device"which issued Jul. 20, 1982, to Rudy, which is expressly incorporatedherein by reference, discloses selectively permeable sheets of film thatare formed into a bladder and inflated with a gas or mixture of gases toa prescribed pressure. The gas or gases utilized ideally have arelatively low diffusion rate through the selectively permeable bladderto the exterior environment while gases contained in the atmosphere,such as nitrogen, oxygen, and argon, have a relatively high diffusionrate are able to penetrate the bladder. This produces an increase in thetotal pressure within the bladder, by the addition of the partialpressures of the nitrogen, oxygen and argon from the atmosphere to thepartial pressures of the gas or gases with which the bladder isinitially inflated. This concept of a relative one-way addition of gasesto enhance the total pressure of the bladder is now known as "diffusionpumping."

Many of the earlier midsole bladders used in the footwear manufacturingindustry prior to and shortly after the introduction of the Air-Solemathletic shoes consisted of a single layer gas barrier type film madefrom polyvinylidene chloride-based materials such as Saran® (which is aregistered trademark of the Dow Chemical Co.) and which by their natureare rigid plastics, having relatively poor flex fatigue, heatsealability and elasticity. Composite films of two gas barrier materialshave also been used. Momose, U.S. Pat. No. 5,122,322, incorporatedherein by reference, describes a film of a first thermoplastic resinhaving a plurality of continuous tapes of a second thermoplastic resinthat lie parallel to the plane of the film. The first thermoplasticresin is selected from polyolefin, polystyrene, polyacrylonitrile,polyester, polycarbonate, or polyvinyl chloride resins and modifiedresins. The second resin may be a polyamide, saponified ethylene vinylacetate copolymer, ethylene-vinyl alcohol copolymer, polyvinylidenechloride, or polyacrylonitrile copolymer. The film is formed byextruding the first resin from a first extruder and the second resinfrom a second extruder, introducing both extrudate streamssimultaneously into a static mixer in which the layers (tapes) areformed. The film may have one or two outer films laminated to it. Whilethese films are disclosed to have an oxygen permeation rate of 0.12 to900 cc/m² -day-atm at 20° C., making them generally suitable for formingcushioning material for packaging and shipping material, the films arenot resilient or flexible enough for cushioning bladders for footwear.

Additional laminates of two different kinds of barrier materials, inwhich the laminate has a large number of relatively thin layers of thedifferent materials, have been disclosed. Schrenk et al., U.S. Pat. No.3,565,985, 4,937,134, 5,202,074, 5,094,788, and 5,094,793, 5,380,479,5,540,878, 5,626,950; Chisolm et al., U.S. Pat. No. 3,557,265;Ramanathan et al., and U.S. Pat. No. 5,269,995, all of which areincorporated herein by reference (including the references citedtherein), disclose methods of preparing multilayer films (at least about10 layers) using streams of at least two different thermoplastics. Thestreams of molten thermoplastic resin are combined in a layered streamand then directed through a layer multiplying means to provide themultilayer film. The multilayering described in these patents is used toobtain iridescent films. In order to create the iridescent effect, thelayers responsible for the iridescence must have a thickness of 0.05micron to 5 microns. The different thermoplastic materials are chosen tohave a maximum difference in refractive index to achieve maximumiridescence in the multilayer film. The gas barrier materials do notproduce films capable of absorbing repeated impacts without deformationor fatigue failure as is required for membranes of an inflatable bladderor a cushioning device.

Known bladder films that are composites or laminates can also present awide variety of problems in shoe bladders, such as layer separation,peeling, gas diffusion or capillary action at weld interfaces, lowelongation leading to wrinkling of the inflated product, cloudyappearing finished bladders, reduced puncture resistance and tearstrength, resistance to formation via blow-molding and/or heat-sealingand RF welding, high cost processing, and difficulty with foamencapsulation and adhesive bonding, among others. Some previously knownmulti-layer bladders used tie-layers or adhesives in preparing laminatesin order to achieve interlayer bond strength high enough to avoid theproblems mentioned. The use of such tie layers or adhesives, however,generally prevents regrinding and recycling of any waste materialscreated during product formation back into an usable product, makingmanufacturing more expensive and producing more waste. Use of adhesivealso increases the cost and complexity of preparing laminates. These andother perceived short comings of the prior art are described in moreextensive detail in U.S. Pat. Nos. 4,340,626; 4,936,029 and 5,042,176,each of which are hereby expressly incorporated by reference.

Besides combinations of two gas barrier layers, composites may be formedfrom layers of materials having very different properties. Composites ofdifferent materials are particularly useful for footwear bladdersbecause many requirements, sometimes contradictory, are made of themembranes used for footwear bladders. For instance, the membrane mustexhibit excellent gas barrier properties as already mentioned towardboth the inflationary gas and the ambient gases, while at the same timethe membrane must be elastic and be resistant to fatigue failure.Materials used to construct footwear bladders must further be resistantto degradation from the fluids contained and from the environment towhich the footwear is exposed. The problem of diverse and sometimescontradictory property requirements for membranes or films of this sorthas commonly been addressed by creating laminates of at least two layersof distinct materials, one layer providing the durable flexibility of anelastomer and the other providing the fluid barrier property.

One approach has been to react or blend together at least two distinctmaterials to allow each of the different materials to make itsrespective contributions to the properties of the grafted copolymer orblend layer. Moureaux, U.S. Pat. No. 5,036,110, incorporated herein byreference, is an example of a grafted copolymer composition. Moureauxdiscloses a resilient membrane for a hydropnuematic accumulator thatincludes a film of a graft copolymer of a thermoplastic polyurethane andan ethylene vinyl alcohol copolymer. The ethylene vinyl alcoholcopolymer is from 5 to 20% of the graft copolymer. The ethylene vinylalcohol copolymer is dispersed in the polyurethane polymer and there issome grafting between the two polymers. The graft copolymer formsislands of ethylene vinyl alcohol copolymer in the polyurethane matrix.The film is a center layer between two layers of thermoplasticpolyurethane in the membrane of the hydropnuematic. While the nitrogenpermeation rate is reduced as compared to unmodified polyurethane, amatrix film that includes particles of gas barrier resin does not offera gas transmission rate as low as for a composite film that has acontinuous layer of the fluid barrier material.

In an alternate approach, laminates have been described that eliminateadhesive tie layers by providing membranes including a first layer of athermoplastic elastomer, such as a thermoplastic polyurethane, and asecond layer including a barrier material, such as a copolymer ofethylene and vinyl alcohol, wherein hydrogen bonding occurs over asegment of the membranes between the first and second layers. Suchlaminates with layers of flexible materials and layers of fluid barriermaterials are described, for example, in U.S. Pat. No. 5,713,141, issuedFeb. 3, 1998, incorporated herein by reference, and in copending U.S.applications Ser. No. 08/299,287, filed Aug. 31, 1994, entitled"Cushioning Device with Improved Flexible Barrier Membrane;" Ser. No.08/684,351, filed Jul. 19, 1996, entitled "Laminated Resilient FlexibleBarrier Membranes;" Ser. No. 08/475,276, filed Jun. 7, 1995, entitled"Barrier Membranes Including a Barrier Layer Employing AliphaticThermoplastic Polyurethanes;" Ser. No. 08/475,275, filed Jun. 7, 1995,entitled "Barrier Membranes Including a Barrier Layer EmployingPolyester Polyols;" and Ser. No. 08/571,160, filed Dec. 12, 1995,entitled "Membranes of Polyurethane Based Materials Including PolyesterPolyols," each of which is incorporated herein by reference. While themembranes disclosed in these references provide flexible, "permanently"inflated, gas-filled shoe cushioning components that are believed tooffer a significant improvement in the art, still further improvementsare offered according to the teachings of the present invention.

It is an object of the invention to provide membranes and membranematerial that offer enhanced flexibility and resistance to undesirabletransmission of fluids such as an inflationary gas. It is another objectof the invention to provide elastic membranes for inflatable bladdersthat can be inflated with a gas such as nitrogen, in which the membraneprovides a gas transmission rate value of about 10 cubic centimeters persquare meter per atmosphere per day (cc/m² ·atm·day) or less.

SUMMARY OF THE INVENTION

We have now discovered that inflatable bladders with improvedelastomeric properties and low gas transmission rates can be formed frommicrolayer polymeric composites. The microlayer polymeric composites ofthe invention may be used to form a durable, elastomeric membrane forpressurized bladders and other cushioning devices to be used in manyapplications, particularly in footwear or for accumulators. By "durable"it is meant that the membrane has excellent resistance to fatiguefailure, which means that the membrane can undergo repeated flexingand/or deformation and recover without delamination along the layerinterfaces and without creating a crack that runs through the thicknessof the membrane, preferably over a broad range of temperatures. Forpurposes of this invention, the term "membrane" is used to denotepreferably a free-standing film separating one fluid (whether gas orliquid) from another fluid. Films laminated or painted onto anotherarticle for purposes other than separating fluids are preferablyexcluded from the present definition of a membrane.

The microlayer polymeric composite includes microlayers of a firstpolymeric material, also called the structural or elastomeric material,that provide the resiliency and flexibility and microlayers of a secondpolymeric material, also called the fluid barrier material, that providethe low gas transmission rate. For the same overall amount of fluidbarrier material, microlayers of the non-elastomeric fluid barriermaterial produce a more elastomeric, more resilient membrane as comparedto the laminates of the prior art with much thicker layers of thebarrier material.

In particular, the present invention provides an inflatable bladder forapplications such as footwear or hydraulic accumulators, the bladderhaving a membrane that includes at least one layer of the microlayerpolymeric composite of the invention. The microlayer polymeric compositematerial of the invention has rubber-like or elastomeric mechanicalproperties provided by the structural material that allows it torepeatedly and reliably absorb high forces during use withoutdegradation or fatigue failure. It is particularly important inapplications such as footwear and hydraulic accumulator for the membraneto have excellent stability in cyclic loading. The microlayer polymericcomposite material has a low gas transmission rate provided by the gasbarrier material that allows it to remain inflated, and thus to providecushioning, for substantially the expected life of the footwear orhydraulic accumulator without the need to periodically re-inflate andre-pressurize the bladder.

The nitrogen gas transmission rate of the membrane should be less thanabout 10 cubic centimeters per square meter per atmosphere per day(cc/m² ·atm·day). An accepted method of measuring the relativepermeance, permeability and diffusion of different film materials is setforth in the procedure designated as ASTM D-1434-82-V. According to ASTMD-1434-82-V, permeance, permeability and diffusion are measured by thefollowing formulas:

Permeance

(quantity of gas)/[(area)×(time)×(press. diff.)]

=Permeance (GTR)/(press. diff.)

=cc/(sq.m) (24 hr) (Pa)

Permeability

[(quantity of gas)×(film thickness)]/[(area)×(time)×(press.diff.)]

=Permeability [(GTR)×(film thick.)]/(press.diff.)

[(cc)(mil)]/[(m²)(24 hr)(Pa)]

Diffusion (at one atmosphere)

(quantity of gas)/[(area)×(time)]

=Gas Transmission Rate (GTR)

cc/(m²)(24 hr)

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of an athletic shoe with a portion ofthe midsole cut away to illustrate a cross-sectional view;

FIG. 2 is a bottom elevational view of the athletic shoe of FIG. 1 witha portion cut away to expose another cross-sectional view;

FIG. 3 is a section view taken alone line 3--3 of FIG. 1;

FIG. 4 is a fragmentary side perspective view of one embodiment of atubular-shaped, two-layer cushioning device;

FIG. 5 is a sectional view taken along line 4--4 of FIG. 4;

FIG. 6 is a fragmentary side perspective view of a second embodiment ofa tubular-shaped, three-layer cushioning device;

FIG. 7 is a sectional side view taken along line 6--6 of FIG. 6;

FIG. 8 is a perspective view of a membrane embodiment according to thepresent invention formed into a shoe cushioning device;

FIG. 9 is a side view of the membrane illustrated in FIG. 8;

FIG. 10 is a perspective view of a membrane embodiment according to thepresent invention formed into a shoe cushioning device;

FIG. 11 is a side elevational view of a membrane embodiment according tothe present invention formed into a cushioning device which isincorporated into a shoe;

FIG. 12 is a perspective view of the membrane illustrated in FIG. 11;

FIG. 13 is a top elevation view of the membrane illustrated in FIGS. 11and 12;

FIG. 14 is a side elevation view of a membrane embodiment according tothe present invention formed into a cushioning device incorporated intoa shoe;

FIG. 15 is a perspective view of the membrane illustrated in FIG. 14;

FIG. 16 is a top view of the membrane illustrated in FIGS. 14 and 15;

FIG. 17 is a perspective view of a membrane embodiment according to theteachings of the present invention formed into a shoe cushioning device;

FIG. 18 is a side view of the membrane illustrated in FIG. 17;

FIG. 19 is a sectional view of a product formed from a laminatedmembrane according to the teachings of the present invention;

FIG. 20 is a sectional view of a second product manufactured using alaminated membrane according to the teachings of the present invention;

FIG. 21 is a side elevation view of a sheet co-extrusion assembly;

FIG. 22 is a cross-sectional view of the manifold portion of the sheetco-extrusion assembly of FIG. 22;

FIG. 23 is a side elevation view of a tubing co-extrusion assembly;

FIG. 24 is a sectional view of a monolayer tubular membrane;

FIG. 25 is a sectional view of a product formed from a monolayermembrane according to the teachings of the present invention; and

FIG. 26 is a photograph of a cross-section of a microlayer polymericcomposite according to the invention.

DETAILED DESCRIPTION

The bladders of the invention are formed from an elastomeric membranethat includes a layer of a microlayer polymeric composite of the presentinvention. The microlayer polymeric composite of the invention hasalternating thin layers of at least one fluid barrier material and atleast one structural, elastomeric material. Also contemplated aremicrolayer polymeric composites that include layers of different fluidbarrier materials and/or layers of different elastomeric materials, allof the different layers being arranged in regular repeating order. Otherlayers in addition to elastomeric layers and fluid barrier layers thatalternate along with them in a regular, repeating order may optionallybe included. The microlayer polymeric composite should have at leastabout 10 layers. Preferably, the microlayer polymeric composite has atleast about 20 layers, more preferably at least about 30 layers, andstill more preferably at least about 50 layers. The microlayer polymericcomposite can have thousands of layers, and the skilled artisan willappreciate that the number of layers will depend upon such factors asthe particular materials chosen, thicknesses of each layer, thethickness of the microlayer polymeric composite, the processingconditions for preparing the multilayers, and the final application ofthe composite. The microlayer elastomer membranes preferably has fromabout 10 to about 1000 layers, more preferably from about 30 to about1000 and even more preferably it has from about 50 to about 500 layers.

The average thickness of each individual layer of the fluid barriermaterial may be as low as a few nanometers to as high as several mils(about 100 microns) thick. Preferably, the individual layers have anaverage thickness of up to about 0.1 mil (about 2.5 microns). Averagethicknesses of about 0.0004 mil (about 0.01 micron) to about 0.1 mil(about 2.5 microns) are particularly preferable. For example, theindividual barrier material layers can be, on average, about 0.05 mils(about 1.2 microns). The thinner layers of the fluid barrier layermaterial improves the ductility of the bladder membrane.

Elastomeric materials suitable for forming the structural layersinclude, without limitation, polyurethane elastomers, includingelastomers based on both aromatic and aliphatic isocyanates; flexiblepolyolefins, including flexible polyethylene and polypropylenehomopolymers and copolymers; styrenic thermoplastic elastomers;polyamide elastomers; polyamide-ether elastomers; ester-ether orester-ester elastomers; flexible ionomers; thermoplastic vulcanizates;flexible poly(vinyl chloride) homopolymers and copolymers; flexibleacrylic polymers; and blends and alloys of these, such as poly(vinylchloride) alloys like poly(vinyl chloride)-polyurethane alloys. Thedifferent elastomeric materials may be combined as blends in thestructural layers of the microlayer polymeric composite, or may beincluded as separate layers of the microlayer polymeric composite.

Particularly suitable are thermoplastic polyester-polyurethanes,polyether-polyurethanes, and polycarbonate-polyurethanes, including,without limitation, polyurethanes polymerized using as diol reactantspolytetrahydrofurans, polyesters, polycaprolactone polyesters, andpolyethers of ethylene oxide, propylene oxide, and copolymers includingethylene oxide and propylene oxide. These polymeric diol-basedpolyurethanes are prepared by reaction of the polymeric diol (polyesterdiol, polyether diol, polycaprolactone diol, polytetrahydrofuran diol,or polycarbonate diol), one or more polyisocyanates, and, optionally,one or more chain extension compounds. Chain extension compounds, as theterm is used herein, are compounds having two or more functional groupsreactive with isocyanate groups. Preferably the polymeric diol-basedpolyurethane is substantially linear (i.e., substantially all of thereactants are di-functional).

The polyester diols used in forming the preferred thermoplasticpolyurethane of the invention are in general prepared by thecondensation polymerization of polyacid compounds and polyol compounds.Preferably, the polyacid compounds and polyol compounds aredi-functional, i.e., diacid compounds and diols are used to preparesubstantially linear polyester dials, although minor amounts ofmono-functional, tri-functional, and higher functionality materials(perhaps up to 5 mole percent) can be included. Suitable dicarboxylicacids include, without limitation, glutaric acid, succinic acid, malonicacid, oxalic acid, phthalic acid, hexahydrophthalic acid, adipic acid,maleic acid and mixtures of these. Suitable polyols include, withoutlimitation, wherein the extender is selected from the group consistingof ethylene glycol, diethylene glycol, triethylene glycol, tetraethyleneglycol, propylene glycol, dipropylene glycol, tripropylene glycol,tetrapropylene glycol, cyclohexanedimethanol, 2-ethyl-1,6-hexanediol,Esterdiol 204 (sold by Eastman Chemical Co.), 1,4-butanediol,1,5-pentanediol, 1,3-propanediol, butylene glycol, neopentyl glycol, andcombinations thereof. Small amounts of triols or higher functionalitypolyols, such as trimethylolpropane or pentaerythritol, are sometimesincluded. In a preferred embodiment, the carboxylic acid includes adipicacid and the diol includes 1,4-butanediol. Typical catalysts for theesterification polymerization are protonic acids, Lewis acids, titaniumalkoxides, and dialkyltin oxides.

The polymeric polyether or polycaprolactone diol reactant used inpreparing the preferred thermoplastic polyurethanes reacting a diolinitiator, e.g., ethylene or propylene glycol, with a lactone oralkylene oxide chain-extension reagent. Preferred chain-extensionreagents are epsilon caprolactone, ethylene oxide, and propylene oxide.Lactones that can be ring opened by an active hydrogen are well-known inthe art. Examples of suitable lactones include, without limitation,ε-caprolactone, γ-caprolactone, β-butyrolactone, β-propriolactone,γ-butyrolactone, α-methyl-γ-butyrolactone, β-methyl-γ-butyrolactone,γ-valerolactone, δ-valerolactone, γ-decanolactone, δ-decanolactone,γ-nonanoic lactone, γ-octanoic lactone, and combinations of these. Inone preferred embodiment, the lactone is ε-caprolactone. Lactones usefulin the practice of the invention can also be characterized by theformula: ##STR1## wherein n is a positive integer of 1 to 7 and R is oneor more H atoms, or substituted or unsubstituted alkyl groups of 1-7carbon atoms. Useful catalysts include, those mentioned above forpolyester synthesis. Alternatively, the reaction can be initiated byforming a sodium salt of the hydroxyl group on the molecules that willreact with the lactone ring.

In another embodiment of the invention, a diol initiator is reacted withan oxirane-containing compound to produce a polyether diol to be used inthe polyurethane polymerization. The oxirane-containing compound ispreferably an alkylene oxide or cyclic ether, especially preferably acompound selected from ethylene oxide, propylene oxide, butylene oxide,tetrahydrofuran, and combinations of these. Alkylene oxide polymersegments include, without limitation, the polymerization products ofethylene oxide, propylene oxide, 1,2-cyclohexene oxide, 1-butene oxide,2-butene oxide, 1-hexene oxide, tert-butylethylene oxide, phenylglycidyl ether, 1-decene oxide, isobutylene oxide, cyclopentene oxide,1-pentene oxide, and combinations of these. The alkylene oxidepolymerization is typically base-catalyzed. The polymerization may becarried out, for example, by charging the hydroxyl-functional initiatorand a catalytic amount of caustic, such as potassium hydroxide, sodiummethoxide, or potassium tert-butoxide, and adding the alkylene oxide ata sufficient rate to keep the monomer available for reaction. Two ormore different alkylene oxide monomers may be randomly copolymerized bycoincidental addition and polymerized in blocks by sequential addition.Homopolymers or copolymers of ethylene oxide or propylene oxide arepreferred.

Tetrahydrofuran polymerizes under known conditions to form repeatingunits

    --[CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 O]--

Tetrahydrofuran is polymerized by a cationic ring-opening reaction usingsuch counterions as SbF₆ ⁻⁻, AsF₆ ⁻⁻, PF₆ ⁻⁻, SbCl₆ ⁻⁻, BF₄ ⁻⁻, CF₃ SO₃⁻⁻, FSO₃ ⁻⁻, and ClO₄ ⁻⁻. Initiation is by formation of a tertiaryoxonium ion. The polytetrahydrofuran segment can be prepared as a"living polymer" and terminated by reaction with the hydroxyl group of adiol such as any of those mentioned above.

Aliphatic polycarbonate diols are prepared by the reaction of diols withdialkyl carbonates (such as diethyl carbonate), diphenyl carbonate, ordioxolanones (such as cyclic carbonates having five- and six-memberrings) in the presence of catalysts like alkali metal, tin catalysts, ortitanium compounds. Useful diols include, without limitation, any ofthose already mentioned. Aromatic polycarbonates are usually preparedfrom reaction of bisphenols, e.g., bisphenol A, with phosgene ordiphenyl carbonate.

The polymeric diol, such as the polymeric polyester diols describedabove, which are used in the polyurethane synthesis preferably have anumber average molecular weight (determined for example by the ASTMD-4274 method) of from about 300 to about 4,000; more preferably fromabout 400 to about 3,000; and still more preferably from about 500 toabout 2,000. The polymeric diol generally forms a "soft segment" of theelastomeric polyurethane.

The synthesis of the elastomeric polyurethane may be carried out byreacting one or more of the above polymeric diols, one or more compoundshaving at least two isocyanate groups, and, optionally, one or morechange extension agents. The elastomeric polyurethanes are preferablylinear and thus the polyisocyanate component preferably is substantiallydi-functional. Useful diisocyanate compounds used to prepare thethermoplastic polyurethanes of the invention, include, withoutlimitation, isophorone diisocyanate (IPDI), methylene bis-4-cyclohexylisocyanate (H₁₂ MDI), cyclohexyl diisocyanate (CHDI), m-tetramethylxylene diisocyanate (m-TMXDI), p-tetramethyl xylene diisocyanate(p-TMXDI), ethylene diisocyanate, 1,2-diisocyanatopropane,1,3-diisocyanatopropane, 1,6-diisocyanatohexane (hexamethylenediisocyanate or HDI), 1,4-butylene diisocyanate, lysine diisocyanate,1,4-methylene bis-(cyclohexyl isocyanate), the various isomers oftoluene diisocyanate, meta-xylylenediioscyanate andpara-xylylenediisocyanate, 4-chloro-1,3-phenylene diisocyanate,1,5-tetrahydro-naphthalene diisocyanate, 4,4'-dibenzyl diisocyanate, and1,2,4-benzene triisocyanate, xylylene diisocyanate (XDI), andcombinations thereof. Particularly useful is diphenylmethanediisocyanate (MDI).

Useful active hydrogen-containing chain extension agents generallycontain at least two active hydrogen groups, for example, diols,dithiols, diamines, or compounds having a mixture of hydroxyl, thiol,and amine groups, such as alkanolamines, aminoalkyl mercaptans, andhydroxyalkyl mercaptans, among others. The molecular weight of the chainextenders preferably range from about 60 to about 400. Alcohols andamines are preferred. Typical examples of useful diols that are used aspolyurethane chain extenders include, without limitation,1,6-hexanediol, cyclohexanedimethanol (sold as CHDM by Eastman ChemicalCo.), 2-ethyl-1,6-hexanediol, Esterdiol 204 (sold by Eastman ChemicalCo.), 1,4-butanediol, ethylene glycol and lower oligomers of ethyleneglycol including diethylene glycol, triethylene glycol and tetraethyleneglycol; propylene glycol and lower oligomers of propylene glycolincluding dipropylene glycol, tripropylene glycol and tetrapropyleneglycol; 1,3-propanediol, 1,4-butanediol, neopentyl glycol,dihydroxyalkylated aromatic compounds such as the bis (2-hydroxyethyl)ethers of hydroquinone and resorcinol; p-xylene-α, α'-diol; the bis(2-hydroxyethyl) ether of p-xylene-α, α'-diol; m-xylene-α,α'-diol andthe bis (2-hydroxyethyl) ether and mixtures thereof. Suitable diamineextenders include, without limitation, p-phenylenediamine,m-phenylenediamine, benzidine, 4,4'-methylenedianiline,4,4'-methylenibis (2-chloroaniline), ethylene diamine, and combinationsof these. Other typical chain extenders are amino alcohols such asethanolamine, propanolamine, butanolamine, and combinations of these.Preferred extenders include ethylene glycol, diethylene glycol,triethylene glycol, tetraethylene glycol, propylene glycol, dipropyleneglycol, tripropylene glycol, tetrapropylene glycol, 1,3-propyleneglycol, 1,4-butanediol, 1,6-hexanediol, and combinations of these.

In addition to the above-described difunctional extenders, a smallamount of trifunctional extenders such as trimethylol propane,1,2,6-hexanetriol and glycerol, and/or monofunctional active hydrogencompounds such as butanol or dimethyl amine, may also be present. Theamount of trifunctional extenders and/or monofunctional compoundsemployed would preferably be 5.0 equivalent percent or less based on thetotal weight of the reaction product and active hydrogen containinggroups employed.

The reaction of the polyisocyanate, polymeric diol, and chain extensionagent is typically conducted by heating the components, for example bymelt reaction in a twin screw extruder. Typical catalysts for thisreaction include organotin catalysts such as stannous octoate.Generally, the ratio of polymeric diol, such as polyester diol, toextender can be varied within a relatively wide range depending largelyon the desired hardness of the final polyurethane elastomer. Forexample, the equivalent proportion of polyester diol to extender may bewithin the range of 1:0 to 1:12 and, more preferably, from 1:1 to 1:8.Preferably, the diisocyanate(s) employed are proportioned such that theoverall ratio of equivalents of isocyanate to equivalents of activehydrogen containing materials is within the range of 0.95:1 to 1.10:1,and more preferably, 0.98:1 to 1.04:1. The polymeric diol segmentstypically are from about 35% to about 65% by weight of the polyurethanepolymer, and preferably from about 35% to about 50% by weight of thepolyurethane polymer.

It may be desirable under certain applications to include blends ofpolyurethanes to form the structural layers of the microlayer polymericcomposite, such as when susceptibility to hydrolysis is of particularconcern. For example, a polyurethane including soft segments ofpolyether diols or polyester diols formed from the reaction mixture of acarboxylic acid and a diol wherein the repeating units of the reactionproduct has more than eight carbon atoms can be blended withpolyurethanes including polyester diols having repeating units of eightor less carbon atoms or products of branched diols. Preferably, thepolyurethanes other than those including polyester diol repeating unitshaving eight or less carbon atoms or with oxygen atoms connected totertiary carbons will be present in the blends in an amount up to about30 wt.%, (i.e. 70.0 wt.% polyethylene glycol adipate based polyurethane30.0% isophthalate polyester diol based polyurethane). Specific examplesof the polyester diols wherein the reaction product has more than eightcarbon atoms include poly(ethylene glycol isophthalate),poly(1,4-butanediol isophthalate) and poly(1,6-hexanediol isophthalate).

As an alternative to blends of various thermoplastic polyurethanes, asingle polyurethane having various soft segments may be used. Again,without intending to be limiting, the soft segments may include, inaddition to soft segments having a total of eight carbon atoms or less,polyether diols, polyester diols having a total of more than eightcarbon atoms, or mixtures thereof. It is contemplated that the totalamount of soft segment constituency which includes the reaction productof a carboxylic acid and a diol having a total carbon atom count of morethan eight, be present in an amount of up to about 30 wt.% of the totalweight of soft segments included in the polyurethane. Thus, at least 70wt.% of the soft segment repeating units will be the reaction productsof carboxylic acid and a diol, wherein the total carbon atom count forthe reaction product is eight or less.

It should also be noted that there are a number of ways to addpolyurethanes with up to 30 wt.% of polyesters with repeat unitscontaining more than eight carbon atoms to the polyurethanes of thisinvention. Thirty percent or less of a polyurethane derived frompolyester diols containing repeat units with more than eight carbons canbe blended as finished polymers with 70 wt.% or more of polyurethanesderived from polyester diols with repeat units containing eight or lesscarbon atoms, or a single polyurethane could be prepared from a mixtureof polyester diols wherein 70 wt.% or more contain repeat units witheight carbons or less and the balance contains repeat units with morethan eight carbons as described previously. A polyurethane could beprepared from a single diol prepared by reaction from dicarboxylic acidsand diols such that 70 wt.% of the repeat units in the polyester diolcontain eight or less carbon atoms. Combinations of these techniques arealso possible. Among the acids that contain more than six carbon atomsthat could be employed are isophthalic and phthalic acids.

Among the numerous thermoplastic polyurethanes which are useful informing the outer layer 32, polyurethanes such as all of which areeither ester or ether based, have proven to be particularly useful.

Specific examples of suitable materials include polyamide-etherelastomers marketed under the tradename PEBAX® by Elf Atochem,ester-ether elastomers marketed under the tradename HYTREL® by DuPont,ester-ester and ester-ether elastomers marketed under the tradenameARNITEL® by DSM Engineering, thermoplastic vulcanizates marketed underthe tradename SANTOPRENE® by Advanced Elastomeric Systems, elastomericpolyamides marketed under the tradename GRILAMID® by Emser, andelastomeric polyurethanes marketed under the tradename PELLETHANE® byDow Chemical Company, Midland, Mich., ELASTOLLAN® polyurethanes marketedby BASF Corporation, Mt. Olive, N.J., TEXIN® and DESMOPAN® polyurethanesmarketed by Bayer, MORTHANE® polyurethanes marketed by Morton, andESTANE® polyurethanes marketed by B. F. Goodrich Co.

In addition to the elastomeric materials of the structural layers, themicrolayer polymeric composites of the invention include layers of afluid barrier material. Suitable fluid barrier materials include,without limitation, ethylene vinyl alcohol copolymers, poly(vinylchloride), polyvinylidene polymers and copolymers such as polyvinylidenechloride in particular, polyamides, including amorphous polyamides;acrylonitrile polymers, including acrylonitrile-methyl acrylatecopolymers; polyurethane engineering plastics, polymethylpentene resins;ethylene-carbon monoxide copolymers, liquid crystal polymers,polyethylene terephthalate, polyether imides, polyacrylic imides, andother such polymeric materials known to have relatively low gastransmission rates. Blends and alloys of these materials, such ascombinations of polyimides and crystalline polymers such as liquidcrystal polymers, polyamides and polyethylene terephthalate, andpolyamides with styrenics are also suitable. Ethylene vinyl alcoholcopolymers are preferred, particularly those copolymer in which theethylene copolymer ratio is from about 25 mole percent to about 50 molepercent, and more particularly from about 25 mole percent to about 40mole percent. Ethylene vinyl alcohol copolymers are prepared by fullyhydrolyzing ethylene vinyl acetate copolymers. The different fluidbarrier materials may be combined as blends in the structural layers ofthe microlayer polymeric composite, or may be included as separatelayers of the microlayer polymeric composite.

Examples of suitable specific examples include acrylonitrile copolymerssuch as BAREX®, available from BP Chemicals, Inc.; polyurethaneengineering plastics such as ISOPLAST®, available from Dow ChemicalCorp., Midland, Mich.; ethylene vinyl alcohol copolymers marketed underthe trademarks EVAL® by EVAL Company of America (EVALCA), Lisle, Ill.,SOARNOL® by Nippon Goshei Co., Ltd. (U.S.A.) of New York, N.Y., CLARENE®by Solvay, and SELAR® OH by DuPont; polyvinylidiene chloride availablefrom Dow Chemical under the tradename SARAN®, and from Solvay under thetradename IXAN®; liquid crystal polymers such as VECTRA® from HoechstCelanese and XYDAR® from Amoco Chemicals; MDX®6 nylon, available fromMitsubishi Gas Chemical Co., Ltd, Solvay, and Toyobo and amorphousnylons such as NOVAMID® X21 from Mitsubishi, SELAR® PA from DuPont, andGELON A-100 from General Electric Company; KAMAX® polyacrylic-imidecopolymer available from Rohm & Haas; polyetherimides sold under thetradename ULTEM® by General Electric; VINEX poly(vinyl alcohol)available from Air Products; and polymethylpentene resins available fromPhillips 66 Company under the tradename CRYSTALOR and from MitsuiPetrochemical Industries under the tradename TPX®v. Highly preferredcommercially available copolymers of ethylene and vinyl alcohol, such asthose available from EVAL, will typically have an average ethylenecontent of between about 25 mol% to about 48 mol%.

One further feature of the microlayer polymeric composites of thepresent invention is the enhanced bonding which can occur between thelayers of the elastomeric material and the fluid barrier material. Thisso-called enhanced bonding is generally accomplished by using materialsfor both layers that have available functional groups with hydrogenatoms that can participate in hydrogen bonding such as hydrogen atoms inhydroxyl groups or hydrogen atoms attached to nitrogen atoms inpolyurethane groups and various receptor groups such as oxygen atoms inhydroxyl groups, carbonyl oxygens in polyurethane groups and estergroups, and chlorine atoms in PVDC, for example. Such microlayerpolymeric composites are characterized in that hydrogen bonding isbelieved to occur between the elastomeric and fluid barrier materialsthat form the alternating layers. For example, the above describedhydrogen bonding is believed to occur when the elastomeric materialcomprises a polyester diol based polyurethane and the fluid barriermaterial includes a polymer selected from the group consisting ofco-polymers of ethylene and vinyl alcohol, polyvinylidene chloride,co-polymers of acrylonitrile and methyl acrylate, polyethyleneterephthalate, aliphatic and aromatic polyamides, crystalline polymersand polyurethane engineering thermoplastics. In addition to the hydrogenbonding, it is theorized that there will also generally be a certainamount of covalent bonding between the layers of the elastomeric firstmaterial and the fluid barrier second material if, for example, thereare polyurethanes in adjacent layers or if one of the layers includespolyurethane and the adjacent layer includes a barrier material such ascopolymers of ethylene and vinyl alcohol. Still other factors such asorientation forces and induction forces, otherwise known as van derWaals forces, which result from London forces existing between any twomolecules and dipole-dipole forces which are present between polarmolecules are believed to contribute to the bond strength betweencontiguous layers of thermoplastic polyurethane and the main layer.

In addition to the elastomeric polymer and the barrier polymer, thelayers of the microlayer polymeric composite may include variousconventional additives including, without limitation, hydrolyticstabilizers, plasticizers, antioxidants, UV stabilizers, thermalstabilizers, light stabilizers, organic anti-block compounds, colorants(including pigments, dyes, and the like), fungicides, antimicrobials(including bacteriocides and the like), mold release agents, processingaids, and combinations of these. Examples of hydrolytic stabilizersinclude two commercially available carbodiimide based hydrolyticstabilizers known as STABAXOL P and STABAXOL P-100, which are availablefrom Rhein Chemie of Trenton, N.J. Other carbodiimide- orpolycarbodiimide-based hydrolytic stabilizers or stabilizers based onepoxidized soy bean oil may be useful. The total amount of hydrolyticstabilizer employed will generally be less than 5.0 wt.% of thecomposition's total.

Plasticizers can be included for purposes of increasing the flexibilityand durability of the final product as well as facilitating theprocessing of the material from a resinous form to a membrane or sheet.By way of example, and without intending to be limiting, plasticizerssuch as those based on butyl benzyl phthalate (which is commerciallyavailable, e.g. as Santicizer 160 from Monsanto) have proven to beparticularly useful. Regardless of the plasticizer or mixture ofplasticizers employed, the total amount of plasticizer, if any, willgenerally be less than 20.0 wt.% of the total composition.

The alternating layers of the structural polymer and the fluid barrierpolymer have their major surfaces aligned substantially parallel to themajor surfaces of the composite. There are a sufficient number of layersof the fluid barrier polymer so that the microlayer composite has thedesired fluid transmission rate.

The multilayer polymeric composites may be formed by at least twodifferent methods. In a first process, the multilayer polymericcomposites of the invention can be prepared using a two-layer,three-layer, or five-layer feed block that directs the layered streaminto a static mixer or layer multiplier. The static mixer has multiplemixing elements, preferably at least about 5 elements, that increasesthe number of layers geometrically.

In a second method, the multilayer polymeric composites of the inventioncan be prepared by providing a first stream comprising discrete layersof polymeric material. A preferred embodiment of this method isdescribed in detail in Schrenk, et al., U.S. Pat. No. 5,094,793, issuedMar. 10, 1992, which is incorporated herein in its entirety byreference. Briefly, the first stream comprising discrete layers canagain be formed by directing the molten extrudate from extrudersseparately containing the elastomeric material and the fluid barriermaterial into a two-layer, three-layer, or five-layer feed block. Thefirst stream is then divided into a plurality of branch streams, thebranch streams are then redirected or repositioned and individuallysymmetrically expanded and contracted, being finally recombined in anoverlapping relationship to form a second stream with a greater numberof discrete layers. In addition, protective boundary layers may beincorporated according the method of Ramanathan et al., U.S Pat. No.5,269,995, issued Dec. 14, 1993, which is incorporated herein in itsentirety by reference. The protective layers protect the structural andfluid barrier layers from instability and breakup during the layerformation and multiplication. The protective layers are provided by asteam of molten thermoplastic material which is supplied to the exteriorsurfaces of the composite stream to form a protective boundary layer atthe wall of the coextrusion apparatus. The protective layer may addspecial optical or physical attributes to the microlayer polymericcomposite material, such as special coloration, including metalliccoloration obtained by including metallic or other flake pigments in theprotective boundary layer.

Although it is not necessary for all of the layers to be completelayers, that is to extend in the plane of that layer to all edges of thepiece, it is desirable for most layers to be substantially completelayers, that is to extend to the edges of the membrane.

The elastomeric membrane of the invention includes the microlayerpolymeric composite, either as an only layer or as one layer in alaminate construction. The membrane may be of any convenient length andwidth for forming the desired footwear bladder or hydraulic accumulator.The average thickness of the microlayer polymeric composite of themembrane may vary widely, but it may be, for example, from about 3 mils(about 75 microns) to about 200 mils (about 0.5 cm). Preferably, theaverage thickness of the microlayer polymeric composite is at leastabout 50 microns, preferably from about 75 microns to about 0.5 cm, morepreferably from about 125 microns to about 0.5 cm, and particularlypreferably from about 125 microns to about 0.15 cm. When the microlayerpolymeric composite is to be used to prepare a bladder for footwear itis preferred that the microlayer material have an average thickness offrom about 3 mils (about 75 microns) to about 40 mils (about 0.1 cm),while membranes used in hydropneumatic accumulators are usually thicker.In one preferred embodiment the microlayer polymeric composite has anaverage thickness of at least about 125 microns.

The membrane of the invention can be a laminate that includes themicrolayer polymeric material as one or more laminate layers.Preferably, the alternate layers are selected from the polymers listedabove as suitable as the structural material of the microlayer material,and more preferably the alternate layers are polyurethane materials. Anynumber of microlayer layers, preferably from one to about 5, morepreferably one to three are used as alternate layers of the laminate.The other layers of the laminate preferably as elastomeric and includethermoplastic elastomers selected from those already mentioned assuitable for the structural layers of the microlayer polymericcomposite. One preferred membrane of the invention is a laminate thatincludes at least one layer A of an elastomeric polyurethane and atleast one layer B of the microlayer polymeric composite. In otherpreferred embodiment, the membrane is a laminate having layers A-B-A orlayers A-B-A-B-A.

When the microlayer polymeric film is used to prepare a laminate, thelaminate may have an average thickness of from about 3 mils (about 75microns) to about 200 mils (about 0.5 cm), and preferably it has anaverage thickness of from about 3 mils (about 75 microns) to about 50mils (about 0.13 cm). The microlayer polymeric film layer of thelaminate is preferably from about 0.25 mil (about 6.35 microns) to about102 mils (2600 microns).

A bladder may be produced by RF (radio frequency) welding two sheets ofthe microlayer material or microlayer-containing laminate, particularlywhen one layer is a polar material such as a polyurethane. Nonpolarmaterials such as polyolefins can be welded using ultrasound or heatsealing techniques. Other well-known welding techniques may also beemployed.

When used as cushioning devices in footwear such as shoes, the bladdermay be inflated, preferably with nitrogen, to an internal pressure of atleast about 3 psi and up to about 50 psi. Preferably the bladder isinflated to an internal pressure of from about 5 psi to about 35 psi,more preferably from about 5 psi to about 30 psi, still more preferablyfrom about 10 psi to about 30 psi, and yet more preferably from about 15psi to about 25 psi. It will be appreciated by the skilled artisan thatin applications other than footwear applications the desired andpreferred pressure ranges may vary dramatically and can be determined bythose skilled in that particular field of application. Accumulatorpressures, for example, can range up to perhaps 1000 psi.

Preferably, the membranes described herein may be useful for formingcushioning components for footwear. In such applications, the membranespreferably are capable of containing a captive gas for a relatively longperiod of time. In a highly preferred embodiment, for example, themembrane should not lose more than about 20% of the initial inflated gaspressure over a period of approximately two years. In other words,products inflated initially to a steady state pressure of between 20.0to 22.0 psi should retain pressure in the range of about 16.0 to 18.0psi for at least about two years.

The inflationary gas transmission rate of the material for theinflationary gas, which is preferably nitrogen gas, should be less than10 cubic centimeters per square meter per atmosphere per day (cc/m²·atm·day), preferably less than about 3 cc/m² ·atm·day, and particularlypreferably less than about 2 cc/m² ·atm·day.

The microlayer polymeric composites provide increased resistance todelamination and cracking. Dividing the barrier layer into numerouslayers increases the resistance of individual layers to cracking. Whilenot wishing to be bound by theory, it is believed that, given the sameexternal dimensions and a constant density of flaws, a laminate withthinner layers will likely contain fewer flaws in each layer. Thus, themicrolayer polymeric composites containing the same amount of barriermaterial overall as a traditional laminate, but having the barriermaterial divided between many more layers than the one layer or fewlayers in the traditional laminate, will contain more barrier materialin uncracked layers than would the traditional laminate if a crackshould develop from each flaw as the material is loaded. In addition, ifa barrier layer in a microlayer composite develops a crack, dissipativeprocesses along the interfaces help to confine the crack to one layer.Fluid transmission rate should not be affected significantly if cracksdevelop within some of the barrier layers because adjacent barrierlayers still force the diffusing species to take a circuitous path inorder to permeate the membrane.

Among these techniques known in the art are extrusion, blow molding,injection molding, vacuum molding, transfer molding, pressure forming,heat-sealing, casting, melt casting, and RF welding, among others.

Referring to FIGS. 1-3, there is shown an athletic shoe, including asole structure and a cushioning device as one example of a productformed from a membrane in accordance with the teachings of the presentinvention. The shoe 10 includes a shoe upper 12 to which the sole 14 isattached. The shoe upper 12 can be formed from a variety of conventionalmaterials including, but not limited to, leathers, vinyls, and nylonsand other generally woven fibrous materials. Typically, the shoe upper12 includes reinforcements located around the toe 16, the lacing eyelets18, the top of the shoe 20 and along the heel area 22. As with mostathletic shoes, the sole 14 extends generally the entire length of theshoe 10 from the toe region 20 through the arch region 24 and back tothe heel portion 22.

The sole structure 14 is shown to include one or more cushioning devicesor bladders 28 according to the invention, which are generally disposedin the midsole of the sole structure. By way of example, the membranes28 of the present invention can be formed into products having variousgeometries such as a plurality of tubular members which are positionedin a spaced apart, parallel relationship to each other within the heelregion 22 of the midsole 26 as illustrated in FIGS. 1-3. The tubularmembers are sealed to contain an injected captive gas. The barrierproperties of the membrane 28 may be provided by a single layer of themicrolayer polymeric composite 30A as shown in FIG. 24 or by themicrolayer polymeric composite layer 30 as shown in FIGS. 4-5 which isdisposed along the inner surface of a thermoplastic elastomer outerlayer 32. As illustrated in FIGS. 8-18, the membranes 28 of the presentinvention, whether monolayer or multi-layer embodiments, can be formedinto a variety of products having numerous configurations or shapes. Asshould be appreciated at this point, membranes 28 which are formed intocushioning devices employed in footwear may either be fully or partiallyencapsulated within the midsole or outsole of the footwear. The bladderis thus incorporated as a portion of the sole and may form at least apart of an outer surface of the shoe at the sole.

Referring again to FIGS. 1-3, a membrane 28 in accordance with teachingsof the present invention is illustrated as being in the form of acushioning device such as those useful as components of footwear. Themembrane 28, according to the embodiment illustrated in FIG. 24,comprises a single layer 30A of a microlayer polymeric composite of anelastomeric material, preferably a material comprising one or morepolyester diol-based polyurethanes and a second material comprising oneor more fluid barrier polymers.

Referring now to FIGS. 6 and 7, an alternative membrane embodiment A inthe form of an elongated tubular shaped multi-layered component isillustrated. The modified membrane A is essentially the same as themembrane 28 illustrated in FIGS. 4 and 5 except that a third layer 34 isprovided contiguously along the inner surface of the layer 30, such thatlayer 30 is sandwiched between an outer layer 32 and an innermost layer34. The innermost layer 34 is also preferably made from a thermoplasticpolyurethane material. In addition to the perceived benefit of enhancedprotection against degradation of layer 30, layer 34 also tends toassist in providing for high quality welds which facilitate theformation of three-dimensional shapes for products such as cushioningdevices useful in footwear.

Membranes such as those shown in FIGS. 1-7 and FIG. 24 are preferablyfabricated from extruded tubes. Lengths of the tubing are continuouslyextruded and typically spooled in about fifty feet lengths whenmanufactured for inflatable bladders for footwear. Sections of thetubing are RF welded or heat sealed to the desired lengths. Theindividual sealed inflatable bladders produced upon RF welding or heatsealing are then separated by cutting through the welded areas betweenadjacent bladders. The bladders can then be inflated to a desiredinitial inflation pressure ranging from 3 psi ambient to 100 psi,preferably in the range of 3 to 50 psi, with the captive gas preferablybeing nitrogen. It should also be noted that the bladders can befabricated from so-called flat extruded tubing as is known in the artwith the internal geometry being welded into the tube.

Other embodiments formed from the membranes described herein are shownin FIGS. 8-10. Sheets or films of extruded monolayer film or co-extrudedtwo layer or three layer film are formed to the desired thicknesses. Forexample, the thickness range of the co-extruded sheets or films ispreferably between 0.5 mils to 10 mils for the layer 30 and between 4.5mils to about 100 mils for the layers 32 and 34, respectively. Formonolayer cushioning device embodiments, the average thickness willgenerally be between 5 mils to about 60 mils and, more preferably,between about 15 mils and to about 40 mils.

Referring to FIGS. 12-16, membranes fabricated into inflatable bladdersby blow molding are shown. To form the bladders, single layer parisonsof the microlayer polymeric composite are extruded or parisons of twolayer or three layer films, one layer being the microlayer polymericcomposite, are co-extruded as illustrated in FIGS. 21-23. Thereafter,the parisons are blown and formed using conventional blow moldingtechniques. The resulting bladders, examples of which are shown in FIGS.12 and 15, are then inflated with the desired captive gas to thepreferred initial inflation pressure and then the inflation port (e.g.inflation port 38) is sealed by RF welding.

Still another embodiment formed from a membrane of the present inventionis shown in FIGS. 17 and 18. The air bladder is fabricated by formingextruded single layer or co-extruded multiple layer tubing having adesired thickness range. The tubing is collapsed to a lay flatconfiguration and the opposite walls are welded together at selectedpoints and at each end using conventional heat sealing or RF weldingtechniques. The cushioning device is then inflated through a formedinflation port 38 to the desired inflation pressure which ranges from 5psi ambient to 100 psi, and preferably from 5 to 50 psi, with a captivegas such as nitrogen.

In addition to employing the membranes of the present invention ascushioning devices or air bladders as described above, still anotherhighly desirable application for the membranes of the present inventionis for accumulators as illustrated in FIGS. 19, 20 and 25.

Referring to FIG. 25, there is shown an accumulator embodiment formedfrom a monolayer membrane as described above. Likewise, referring toFIGS. 19 and 20, there are shown two alternative accumulator embodimentsformed from a multi-layer membrane of the present invention.Accumulators, and more particularly, hydraulic accumulators are used forvehicle suspension systems, vehicle brake systems, industrial hydraulicaccumulators or for other applications having differential pressuresbetween two potentially dissimilar fluid media. The membrane 124separates the hydraulic accumulator into two chambers or compartments,one of which contains a gas such as nitrogen and the other one of whichcontains a liquid. Membrane 124 includes an annular collar 126 and aflexible body portion 128. Annular collar 126 is adapted to be securedcircumferentially to the interior surface of the spherical accumulatorsuch that body portion 128 divides the accumulator into two separatechambers. The flexible body portion 128 moves generally diametricallywithin the spherical accumulator and its position at any given time isdependent upon the pressure of the gas on one side in conjunction withthe pressure of the liquid on the opposite side.

By way of further example, FIG. 20 illustrates a product in the form ofa hydraulic accumulator including a first layer 114 of the microlayerpolymeric composite of the invention. Additionally, the product includeslayers 112 and 116 formed from one or more thermoplastic elastomers. Asshown, the first layer 114 only extends along a segment of the entireaccumulator body portion. It may be desirable to utilize suchembodiments, otherwise referred to herein as "intermittentconstructions" under circumstances where the delamination potentialalong certain segments of a product is greatest. One such location isalong the annular collar 126 of the bladder or diaphragm for hydraulicaccumulators in laminate embodiments. Thus, while the laminate membranesof the present invention are generally more resistant to delaminationand do a better job of preventing gas from escaping along interfacesbetween layers such as those occurring along the annular collar viacapillary action, it should be recognized that the membranes 110described herein can include segments which do not include layer 114.

The membranes as disclosed herein can be formed by various processingtechniques including but not limited to extrusion, profile extrusion,injection molding, and blow molding and may be sealed to form aninflatable bladder by heat sealing or RF welding of the tubing and sheetextruded film materials. Preferably, the materials are combined at atemperature of between about 300° F. to about 465° F. and a pressure ofat least about 200 psi to obtain optimal wetting for maximum adhesionbetween the contiguous portions of the layers 30, 32 and 34 respectivelyand further to enhance hydrogen bonding between the layers wherein thematerials employed are conducive to hydrogen bonding. Multi-layerlaminate membranes are made from films formed by co-extruding themicrolayer polymeric composite material forming layer 30 together withthe elastomeric material comprising layer 32. After forming themulti-layered laminate film materials, the film materials are heatsealed or welded by RF welding to form the resilient, inflatablebladders.

Similarly, the membranes 110 which are subsequently formed into theproducts illustrated in FIGS. 19, 20 and 25, may be co-extrusions giverise to products which appear to demonstrate the above desired hydrogenbonding between the respective layers 114 and, 112 and 116. To form aproduct such as a hydraulic accumulator bladder or diaphragm via amulti-layer process, such as blow molding, any one of a number ofcommercially available blow molding machines such as a Bekum BM502utilizing a co-extrusion head model No. BKB95-3B1 (not shown) or a KrupKEB-5 model utilizing a model No. VW60/35 co-extrusion head (not shown)could be utilized.

The membranes, whether in the form of sheet, substantially closedcontainers, cushioning devices, accumulators or other structures,preferably will have a tensile strength on the order of at least about2500 psi; a 100% tensile modulus of between about 350-3000 psi and/or anelongation of at least about 250% to about 700%.

Sheet can be made by forcing molten polymer formed in the extruderthrough a coat hanger die. Collapsed tubing and parisons used in blowmolding are made by forcing molten plastic generated by an extruderthrough an annular die.

The microlayer polymeric composite can be used as one layer of amultilayer laminate. A multi-layer process known as sheet co-extrusionis also a useful technique to form membranes in accordance with theteachings of the present invention. Sheet co-extrusion generallyinvolves the simultaneous extrusion of two or more polymeric materialsthrough a single die where the materials are joined together such thatthey form distinct, well bonded layers forming a single extrudedproduct.

The equipment required to produce co-extruded sheet consists of oneextruder for each type of resin which are connected to a co-extrusionfeed block such as that shown in FIGS. 21 and 23, which are commerciallyavailable from a number of different sources including the CloerenCompany of Orange, Tex. and Production Components, Inc. of Eau Claire,Wis., among others.

The co-extrusion feed block 150 consists of three sections. The firstsection 152 is the feed port section which connects to the individualextruders and ports the individual round streams of resin to theprogramming section 154. The programming section 154 then reforms eachstream of resin into a rectangular shape the size of which is inproportion to the individual desired layer thickness. The transitionsection 156 combines the separate individual rectangular layers into onesquare port. The melt temperature of each of the TPU layers shouldgenerally be between about 300° F. to about 465° F. To optimize adhesionbetween the respective layers, the actual temperature of each meltstream should be set such that the viscosities of each melt streamclosely match. The combined laminar melt streams are then formed into asingle rectangular extruded melt in the sheet die 158 which preferablyhas a "coat hanger" design as shown in FIG. 22 which is now commonlyused in the plastics forming industry. Thereafter the extrudate can becooled utilizing rollers 160 forming a rigid sheet by either the castingor calendering process.

Similar to sheet extrusion, the equipment required to produceco-extruded tubing consists of one extruder for each type of resin witheach extruder being connected to a common multi-manifolded tubing die.The melt from each extruder enters a die manifold such as the oneillustrated in FIG. 23 which is commercially available from a number ofdifferent sources including Canterberry Engineering, Inc. of Atlanta,Ga. and Genca Corporation of Clearwater, Fla. among others, and flows inseparate circular flow channels 172A and 172B for the different melts.The flow channels are then shaped into a circular annulus the size ofwhich is proportional to the desired thickness for each layer. Theindividual melts are then combined to form one common melt stream justprior to the die entrance 174. The melt then flows through a channel 176formed by the annulus between the outer surface 178 of a cylindricalmandrel 180 and the inner surface 182 of a cylindrical die shell 184.The tubular shaped extrudate exits the die shell and then can be cooledinto the shape of a tube by many conventional pipe or tubing calibrationmethods. While a two component tube has been shown in FIG. 23 it shouldbe understood by those skilled in the art that additional layers can beadded through separate flow channels.

Regardless of the plastic forming process used, it is desirable that aconsistent melt of the materials employed be obtained to accomplishbonding between layers across the intended length or segment of thelaminated product. Again then, the multi-layer processes utilized shouldbe carried out at maintained temperatures of from about 300° F. to about465° F. Furthermore, it is important to maintain sufficient pressure ofat least 200 psi at the point where the layers are joined wherein theabove described hydrogen bonding is to be effectuated.

As previously noted, in addition to the excellent bonding which can beachieved for the laminated membrane embodiments of the presentinvention, another objective, especially with regard to membranesemployed as cushioning devices for footwear, is to provide membraneswhich are capable of retaining captive gases for extended periods oftime. In general, membranes which offer gas transmission rate values of15.0 or less for nitrogen gas as measured according to the proceduresdesignated at ASTM D-1434-82 are acceptable candidates for extended lifeapplications. Thus, while the membranes of the present invention canhave varying thicknesses depending mainly on the intended use of thefinal product, the membranes of the present invention will preferablyhave a gas transmission rate value of 15.0 or less, regardless of thethickness of the membrane. Likewise, while nitrogen gas is the preferredcaptive gas for many embodiments and serves as a benchmark for analyzinggas transmission rates in accordance with ASTM D-1434-82, the membranescan contain a variety of different gases and/or liquids.

In preferred embodiments, the membranes of the present invention willhave a gas transmission rate of 10.0 and still, more preferably, willhave gas transmission rates of 7.5 or less for nitrogen gas. Still morepreferably, the membranes of the present invention will have a gastransmission rate of 5.0 or less and, still more preferably yet, willhave a gas transmission rate of 2.5 or less for nitrogen gas. Under themost highly preferred embodiments, the membranes of the presentinvention will have a gas transmission rate of 2.0 or less for nitrogengas.

In addition to the improved resistance to gas transmission offered bythe various products formed from the polyester diol based polyurethanesdescribed herein, products made from polyester diol based polyurethaneshave also shown a marked improvement in durability over thermoplasticpolyurethanes which do not include polyester polyols.

Upon inflating the cushioning devices to 20.0 psig with nitrogen gas,each sample was intermittently compressed by a reciprocating pistonhaving a 4.0 inch diameter platen. The stroke of each piston wascalibrated to travel a height which would compress each sample to anaverage of 25.0% of the initial inflated height at maximum stroke. Thereciprocating pistons were then allowed to cycle or stroke until a partfailure was detected. Part failure, as the term is used herein, isdefined as a sufficient leakage of the nitrogen gas and deflation of thecushioning device to cause a lever placed in identical locations alongeach of the cushioning devices to contact a microswitch which stops thereciprocating piston stroke. The total number of cycles or strokes werethen recorded for each sample with a high number of strokes beingindicative of a more durable material. Preferably, permanently inflatedcushioning devices should be capable of withstanding at least about200,000 cycles to be considered for applications as footwear components.In addition to a high degree of durability, it is often desirable toform products which are relatively transparent in nature, i.e. productswhich meet certain standards in terms of the yellowness level detectedand the transmission of light through the material. For example,transparency of the product is often a consideration for cushioningdevices such as those utilized as components of footwear wherein thecushioning device is visually accessible. Cushioning devices formed fromPellethane 2355-85 ATP or Pellethane 2355-87AE have proven to be usefulfor shoe components since the material has been shown to offeracceptable levels both in terms of the yellowness level detected and thelight transmission through the material.

While the bladders of the invention have been described for the highlyuseful applications of cushioning devices for footwear and foraccumulators, it should be appreciated that the membranes of the presentinvention have a broad range of applications, including but not limitedto bladders for inflatable objects such as footballs, basketballs,soccer balls, inner tubes; flexible floatation devices such as tubes orrafts; as a component of medical equipment such as catheter balloons; aspart of an article of furniture such as chairs and seats, as part of abicycle or saddle, as part of protective equipment including shin guardsand helmets; as a supporting element for articles of furniture and, moreparticularly, lumbar supports; as part of a prosthetic or orthopedicdevice; as a portion of a vehicle tire, particularly the outer layer ofthe tire; and as part of certain recreation equipment such as componentsof wheels for in-line or roller skates.

Procedure

A microlayer laminate was prepared by the following method. Twoextruders, one for polyurethane elastomer and one for ethylene vinylalcohol copolymer, were connected to a feed block. The molten polymerfrom the extruders fed into the feed block, producing either athree-layer polyurethane/EVOH/polyurethane stream or a five-layerpolyurethane/EVOH/polyurethane/EVOH/polyurethane stream. The stream fromthe feedblock is fed continuously into a static mixer to produce astream with microlayers of polyurethane and EVOH. The microlayer streamwas fed into a sheet die and then onto a three-roll stack. The laminatewas cooled and then slit and wound in line.

EXAMPLE 1

In the above procedure, Pellethane 2355 85ATP (a polyester-polyurethanecopolymer having a Shore A hardness of 85, available from Dow ChemicalCo., Midland, Mich.) was used as the polyurethane and LCF 101A (anethylene-vinyl alcohol copolymer having 32% that is available from Eval,Chicago, Ill.) was used as the EVOH were fed into a five-streamfeedblock. The stream from the feedblock was introduced into a staticmixer having seven elements. The resulting microlayer polymericcomposite had 15% by weight of the LCF 101A and had a thickness of 20mils. FIG. 26 is a photograph of a cross-section of the microlayerpolymeric composite produced, taken using an optical microscope inreflectance mode. The EVOH layers were stained using an iodine solution.The photograph shows at least 28 layers of material.

The physical properties of the microlayer polymeric composite weremeasured.

    ______________________________________                                        Tensile strength      6494 psi                                                Elongation at fail         490%                                               Tensile modulus               44,200 psi                                      50% modulus                       1860 psi                                    100% modulus                     2016 psi                                     200% modulus                     2586 psi                                     300% modulus                     3741 psi                                     ______________________________________                                    

EXAMPLE 2

A microlayer polymeric composite was produced according to Example 1,but having 7.5% by weight of the LCF 101A. The physical properties ofthe microlayer polymeric composite were measured.

    ______________________________________                                        Tensile strength       7569 psi                                               Elongation at fail            545%                                            Tensile modulus                 28,175 psi                                    50% modulus                          1562 psi                                 100% modulus                        1777 psi                                  200% modulus                        2419 psi                                  100% modulus                        3636 psi                                  Gas Transmission Rate      0                                                  (for nitrogen)                                                                ______________________________________                                    

What is claimed is:
 1. A pressurized bladder, comprising an elastomericbarrier membrane enclosing an inflationary gas, wherein:said membranecomprises a microlayer polymeric composite having an average thicknessof at least about 50 microns, wherein said microlayer polymericcomposite includes at least about 10 microlayers, each microlayerindividually up to about 100 microns thick, said microlayers alternatingbetween at least one gas barrier material and at least one elastomericmaterial; and further wherein said membrane has a gas transmission ratetoward the inflationary gas of about 10 cc/m² ·atm·day or less.
 2. Abladder according to claim 1, wherein said elastomeric material includesa member selected from the group consisting of polyurethane elastomers,flexible polyolefins, styrenic thermoplastic elastomers, polyamideelastomers, polyamide-ether elastomers, ester-ether elastomers,ester-ester elastomer, flexible ionomers, thermoplastic vulcanizates,flexible poly(vinyl chloride) homopolymers and copolymers, flexibleacrylic polymers, and combinations thereof.
 3. A bladder according toclaim 1, wherein said elastomeric material includes a polyurethaneelastomer.
 4. A bladder according to claim 1, wherein said elastomericmaterial includes a member of the group consisting of thermoplasticpolyester diol-based polyurethanes, thermoplastic polyether diol-basedpolyurethanes, thermoplastic polycaprolactone diol-based polyurethanes,thermoplastic polytetrahydrofuran diol-based polyurethanes,thermoplastic polycarbonate diol-based polyurethanes, and combinationsthereof.
 5. A bladder according to claim 4, wherein the elastomericmaterial includes a thermoplastic polyester diol-based polyurethane. 6.A bladder according to claim 5, wherein the polyester diol of saidpolyurethane is a reaction product of at least one dicarboxylic acid andat least one diol.
 7. A bladder according to claim 6, wherein thedicarboxylic acid is selected from the group consisting of adipic acid,glutaric acid, succinic acid, malonic acid, oxalic acid, and mixturesthereof.
 8. A bladder according to claim 6, wherein the diol is selectedfrom the group consisting of ethylene glycol, diethylene glycol,triethylene glycol, tetraethylene glycol, propylene glycol, dipropyleneglycol, tripropylene glycol, tetrapropylene glycol, 1,3-propanediol,1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, andmixtures thereof.
 9. A bladder according to claim 6, wherein thecarboxylic acid includes adipic acid and the diol includes1,4-butanediol.
 10. A bladder according to claim 5, wherein thepolyurethane is polymerized using at least one extender compoundselected from the group consisting of diols and diamines.
 11. A bladderaccording to claim 10, wherein the extender is selected from the groupconsisting of ethylene glycol, diethylene glycol, triethylene glycol,tetraethylene glycol, propylene glycol, dipropylene glycol, tripropyleneglycol, tetrapropylene glycol, 1,3-propanediol, 1,4-butanediol,1,6-hexanediol, and mixtures thereof.
 12. A bladder according to claim10, wherein the ratio of equivalents of polyester diol to equivalents ofextender is from about 1:1 to about 1:8.
 13. A bladder according toclaim 1, wherein the fluid barrier material includes a member selectedfrom the group consisting of ethylene vinyl alcohol copolymers,polyvinylidene chloride, acrylonitrile copolymers, polyethyleneterephthalate, polyamides, crystalline polymers, polyurethaneengineering thermoplastics, and combinations thereof.
 14. A bladderaccording to claim 1, wherein the fluid barrier material comprises anethylene vinyl alcohol copolymer.
 15. A bladder according to claim 14,wherein the ethylene vinyl alcohol copolymer has an ethylene copolymerratio of from about 25 mole percent to about 50 mole percent.
 16. Abladder according to claim 14, wherein the ethylene vinyl alcoholcopolymer has an ethylene copolymer ratio of from about 25 mole percentto about 40 mole percent.
 17. A bladder according to claim 1, whereinsaid microlayer polymeric composite includes at least about 50microlayers.
 18. A bladder according to claim 1, wherein said microlayerpolymeric composite includes from about 10 microlayers to about 1000microlayers.
 19. A bladder according to claim 1, wherein said microlayerpolymeric composite includes from about 50 microlayers to about 500microlayers.
 20. A bladder according to claim 1, wherein the averagethickness of each fluid barrier material microlayer is independently upto about 2.5 microns thick.
 21. A bladder according to claim 1, whereinthe average thickness of each fluid barrier material microlayer isindependently from about 0.01 micron to about 2.5 microns thick.
 22. Abladder according to claim 1, wherein the average thickness of themicrolayer polymeric composite is from about 75 microns to about 0.5centimeter.
 23. A bladder according to claim 1, wherein the averagethickness of the microlayer polymeric composite is from about 75 micronsto about 0.1 centimeter.
 24. A bladder according to claim 1, whereinsaid membrane is a laminate comprising at least one layer A including anelastomeric polyurethane and at least one layer B including saidmicrolayer polymeric composite.
 25. A bladder according to claim 23,wherein said laminate comprises layers A-B-A.
 26. A bladder according toclaim 23, wherein said laminate comprises layers A-B-A-B-A.
 27. Abladder according to claim 1, wherein the microlayer polymeric compositeis formed with an outer protective boundary layer.
 28. A bladderaccording to claim 24, wherein said laminate has an average thickness ofup to about 0.5 centimeter.
 29. A bladder according to claim 24, whereinsaid layer B has an average thickness of from about 6.35 microns toabout 2600 microns.
 30. A bladder according to claim 1, wherein saidmembrane has a nitrogen gas transmission rate of less than about 3 cc/m²·atm·day.
 31. A bladder according to claim 1, wherein said membrane hasa nitrogen gas transmission rate of less than about 2 cc/m² ·atm·day.32. A bladder according to claim 1, wherein inflationary gas is at apressure of at least about 3 psi.
 33. A bladder according to claim 1,wherein inflationary gas is at a pressure of from about 3 to about 50.34. A bladder according to claim 1, wherein inflationary gas isnitrogen.
 35. A shoe, comprising at least one pressurized bladderaccording to claim
 32. 36. A shoe according to claim 35, wherein thebladder is incorporated as a portion of said sole.
 37. A shoe accordingto claim 35, wherein said bladder forms at least a part of an outersurface of said shoe.